Ankley Gerald T, Degitz S J, Diamond S A, Tietge J E
Mid-Continent Ecology Division, National Health and Environmental Effects Research Laboratory, Office of Research and Development, US Environmental Protection Agency, 6201 Congdon Boulevard, Duluth, MN 55804-2595, USA.
Ecotoxicol Environ Saf. 2004 May;58(1):7-16. doi: 10.1016/j.ecoenv.2004.01.004.
Several species of anuran amphibians from different regions across North America have recently exhibited an increased occurrence of malformations, predominantly of the hindlimb. Research concerning the potential causes of these malformations has focused extensively on three stressors: chemical contaminants, ultraviolet (UV) radiation, and parasitic trematodes. In this overview of recent work with each of these stressors, we assess their plausibility as contributors to the malformations observed in field-collected amphibians. There is as yet little evidence that chemical contaminants are responsible for the limb malformations. This includes chemicals, such as the pesticide methoprene, that could affect retinoid-signaling pathways that are critical to limb development. Exposure to UV radiation also seems to be an unlikely explanation for hindlimb malformations in amphibians. Although solar UV can cause hindlimb deficiencies in amphibians, a probabilistic assessment based on empirical dose-response and exposure data indicates that UV exposures sufficient to induce limb defects would be uncommon in most wetlands. Results of controlled studies conducted with some affected species and field-monitoring work suggest infection by digenetic trematodes as a promising explanation for the malformations observed in anurans collected from many field sites. Controlled experimentation with additional species and monitoring across a broader range of affected sites are required to assess fully the role of trematodes in relation to other stressors in causing limb malformations. If trematode infestations are indeed related to the recent increases in malformed amphibians, then the question remains as to what alterations in the environment might be causing changes in the distribution and abundance of the parasites.
来自北美不同地区的几种无尾两栖动物最近出现畸形的情况有所增加，主要是后肢畸形。关于这些畸形潜在原因的研究主要集中在三个压力源上：化学污染物、紫外线（UV）辐射和寄生吸虫。在对近期针对每个压力源的研究工作进行的概述中，我们评估了它们作为导致野外采集的两栖动物畸形的因素的合理性。目前几乎没有证据表明化学污染物是肢体畸形的原因。这包括一些化学物质，如杀虫剂烯虫酯，它可能会影响对肢体发育至关重要的视黄酸信号通路。暴露于紫外线辐射似乎也不太可能是两栖动物后肢畸形的原因。虽然太阳紫外线会导致两栖动物后肢缺陷，但基于经验剂量反应和暴露数据的概率评估表明，在大多数湿地中，足以诱发肢体缺陷的紫外线暴露并不常见。对一些受影响物种进行的对照研究结果和野外监测工作表明，复殖吸虫感染是从许多野外地点采集的无尾两栖动物中观察到的畸形的一个有希望的解释。需要对更多物种进行对照实验，并在更广泛的受影响地点进行监测，以全面评估吸虫在导致肢体畸形方面相对于其他压力源的作用。如果吸虫感染确实与近期畸形两栖动物数量的增加有关，那么问题仍然是环境中的哪些变化可能导致寄生虫的分布和数量发生变化。
